To provide an oven cooling structure which can uniformly cool a separation column efficiently without generating any cold spot.

In the front face part of an oven main body 1, inside which a separation column 4 arranged axisymmetrically in a frontal vision, a heater 6 heating the separation column 4, and a fan 7 are provided, a cooling gas inlet 15 opened toward the central part of the inside hollow part of the separation column 4 is arranged. Cooling gas introduced from the inlet 15 is passed through the inside hollow part of the separation column 4 once without being brought into any contact with the separation column 4, and then, reversely stirred and fed toward the separation column 4 by means of the fan 7 so as to cool down the separation column 4.